Cross-sectional geometrical characteristic for the bends along the lower Jingjiang reach

Abstract

The evolution of bar–pool configurations in response to upstream damming has significant impacts on channel regulations, navigations, water intakes and protection projects. This paper reports on and analyses the evolution of bar–pool configurations in bends along the lower Jingjiang reach (LJR) after the impoundment of the Three Gorge dam (TGD), which is distinguished from the natural evolution of the bends. The main factors in the different adjustments of bar–pool configurations are the changes in incoming flow and sediment regime during pre- and post-TGD periods. To capture the changes in the bar–pool configurations, a new cross-sectional geometrical characteristic is presented – relative lateral distance of the centroid (RLDC). RLDC has close relations with the incoming sediment coefficient (i.e. incoming discharge divided by suspended sediment concentration during flood season). RLDC is better than the conventional cross-sectional geometrical characteristic (e.g. width-to-depth ratio) to indicate the bar–pool configurations downstream of large dam projects. Based on the delayed response model, values of RLDC in the bends of the LJR are related to the previous 4–6 years’ incoming sediment coefficient, and the correlation coefficient is about 0.90. RLDC is expected to capture the variations of bar–pool configurations in the bends downstream of the large dam project.